This invention relates to the art of compression tools for joining pipes and couplings and, more particularly, to an improved pivotal jawarm member for a compression tool.
Compression tools for joining tubes or pipes and coupling components are well known as shown, for example, in U.S. Pat. No. 6,035,775 to Nghiem. Such tools include a compression jaw set removably mounted on a drive mechanism by which the jawarms of the set are displaced into compression about a pipe and coupling to join the latter. More particularly, the jaw set is comprised of a pair of jawarm members pivotally mounted between a pair of side plates and having inwardly open opposed jaw recesses at one end and laterally inwardly facing cam surfaces at the opposite ends. The jawarms are pivotal about pins located in openings through the jawarms between the opposite ends thereof, and the jaw set is mountable on the drive mechanism by means of the side plates and at a location relative to the jaw set which is laterally between the pivot pins and between the pivot pins and cam surfaces of the jaw members. The drive mechanism includes cam rollers which are displaceable axially forwardly and rearwardly along the cam surfaces of the jaw members, and when displaced forwardly of the cam surfaces, engage the latter and displace the opposed jaw recesses toward one another and constrictably about a pipe and coupling interposed therebetween.
The jawarm members have laterally inner and outer edges between the opposite ends thereof and, during operation of the jaw set to compressibly join a pipe and coupling, the area of the jawarm member between the pivot pin opening and inner edge and between the jaw recess and cam surface along the inner edge is under tension and the area laterally outwardly thereof is under compression. The side plates are also stressed during operation of the jaw set in that pivotal displacement of the jawarm members about the pivot pins to produce compressive engagement between the jaw recesses imposes laterally outwardly directed forces through the pivot pins to the side plates. At some point during the life of the jaw set, failure will occur and, preferably, will occur in at least one of the side plates. Failure in a side plate is preferred in that, heretofore, the location of a failure in a jawarm member and the direction of fracture thereafter was unpredictable. More particularly in this respect, failure in a jawarm member typically occurred either between a jaw recess and outer side of the jaw member forwardly of the pivot pin opening or between the inner and outer sides at one or more locations rearwardly of the pivot pin opening. Such failures most often result in separation of the jawarm members into distinct pieces and, in an effort to maintain the pieces together following breakage, strap arrangements have been incorporated in the jaw sets and fastened, for example, to the outer sides of the jawarm members so as to retain separated parts of a jaw member in the jaw set environment following a failure. The strap approach to parts retention is expensive and renders the jawarm members as well as the jaw set using such strapped members structurally complex.
One manufacturer of jawarm members for compression tools alleged to have developed a heat treatment process that prevented the separation of a jawarm into pieces upon failure. In this respect, a fracture of the arm from the inner side toward the outer side thereof allegedly resulted in the material of the arm adjacent the outer side acting as a hinge between the arm parts on opposite sides of the line of fracture. Thus, instead of entirely separating, the parts allegedly remained interconnected following breakage. A number of the latter jawarms were tested for determining the veracity of the alleged non-separating effect. These jawarms, which are shown in U.S. Pat. No. 6,434,998 to Amherd, include a spring and pin recess along the inner edge, for a jaw set using the jawarms to accommodate a torsion spring arrangement therebetween, and a mounting pin clearance recess spaced rearwardly from the spring and pin recess. As the result of testing 38 of the foregoing jaws of different sizes, it was noted that a majority of the jaw members of each size failed from the spring and pin recess to the pivot pin opening through the jaw member. However, the location of failure was still unpredictable in that failures in from about 14% to 25% of each of the different sizes of jawarms tested occurred at the mounting pin clearance recess and across the jawarm arm to the outer side thereof. Moreover, in most of the jawarms tested, the failure at the mounting pin clearance resulted in breakage of the arm into separate pieces. Accordingly, there was no consistency with regard either to predictability of the location of jaw failure or control of the point of failure along the jawarm and direction of the line of fracture from the point of failure.